#define _CRT_SECURE_NO_WARNINGS 520
#include<stdio.h>

int main()
{
	int a[] = { 1,2,3,4,5,1,2,3,4 };
	int ans = 0;
	int sz = sizeof(a) / sizeof(a[0]);
	for (int i = 0; i < sz; i++)
	{
		ans ^= a[i];   //1^2^3^4^5^1^2^3^4 = (1^1)^(2^2)^(3^3)^(4^4)^5 = 0^0^0^0^5 = 5
	}
	printf("%d", ans);
	return 0;
}